The evolution of black hole states(6)

We discuss the evolution of black hole transients on the basis of a few systems that were intensively observed with the Rossi X-ray Timing Explorer. We focus on the global evolution and the observed state transitions. Rather than giving a numerical recipe

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Figure3.Examplesofpower-densityspectraofGX339-4fromthefourstatesdiscussedinthetext.

Attheendofthe2002/2003outburstGX339-4returnedtothehardstate,similartowhatisobservedinmost,ifnotall,blackholetransients.IntheHIDthiscanbenicelyseenasthelowerhorizontalbranchbendingdowntostartrunningparallelto,andinfactnearlyontopof,thehardstatebranchthatwastracedoutduringtherise.Such‘saturation’ofthespectralhardnesswasalsoobservedinXTEJ1650–500(Rossietal.,2003,seealsoFig.1).ItisinterestingtonotethatonceGX339-4reachedthehardnessatwhichitoriginallyleftthehardstatebranch,theoptical/IRshowedastrongincrease(seelightcurvesinBailynandFerrara,2004),indicatingthatthejetdoesnotbecomevisibleintheoptical/IR(orswitchon)untilthehardstatebranchisreached(aswasalreadysuggestedbyKalemcietal.,2004basedonobservations4U1543–47).Thespectralhardeningtowardsthehardstateisnotnecessarilyamonotonicprocess,ascanbeseenintheHIDofGX339-4andXTEJ1859+226.

ObservationsofhardstatebranchesextendingovermanyordersofmagnitudeinGX339-4andXTE1650–500indicatethatthehardstateaccretion owgeometry(whichlikelygivesrisetostrongout ows)canexistoverawiderangeinmassaccretionrate.

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